256 



FIRST YEAR SCIENCE 



duckbill, the lowest of all quadrupeds, which in its char- 

 acteristics resembles both quadrupeds and birds. 



All this seems to show that the distribution and devel- 

 opment of the animals of the different continents have been 

 largely dependent upon the former geographical relations 

 of the land masses. The native animals of a region are 

 not necessarily the only ones suited to it ; animals from 

 other places may be even better adapted, but they have 

 been kept out by some natural barrier. This is particu- 

 larly evident in the case of Australia, where the weak 

 native animals would have been readily displaced by the 

 stronger animals of Asia could these have reached that 

 isolated continent. 



118. Life as Affected by Climate. Climate has had a 

 great effect upon the distribution and development of life. 



TIMBER LINE ON A HIGH MOUNTAIN. 



But the life on the earth cannot be grouped into climatic 

 belts, as certain animals and plants are able to endure a 



